Lensun 20W 12V Black Fiberglass Semi-Flexible Monocrystalline Solar Panel for 12V Charge Battery on Boats, Caravans, Motorhomes, Yachts, RVs The panel uses a more expensive material (imported from Japan) called ETFE (Ethylene Tetrafluoroethylene) versus PET (Polyethylene terephthalate). The ETFE film layer absorbs light better with less reflection leading to more power per square inch. Made of Fiberglass back sheet. The ETFE material bonded with the fiberglass back sheet makes a stronger panel than a cheaper PET film one with less chance of cracking or water intrusion. Highly stain-resistant and easily gets cleaned by the rain. Highly resistant to seawater corrosion. Waterproof and highly resistant to the harsh operating conditions of a marine environment.